Hello, my Unifoil Katana mast head has worn down (the part that inserts into the fuselage) and the foils wobble until the screws are tightened and then slowly back out the screws over time during my sessions.
Anyone have any suggestions of the best way to fix this problem? Epoxy filler?
One option is to sand down the bottom of the mast so that it no longer bottoms out in the fuselage.
Seconding the request for any technical beta on “repotting” a carbon mast in an aluminum fuse…in my case it’s an Axis masthead that’s slowly been wearing away. The aluminum tape fix seems an inelegant half-measure.
That’s the idea. Can’t find one for a mast in a quick search. It’s the same process though. @toomuchepoxy will just tell you to epoxy the whole thing together. 
I potted my fuse-to-front wing connections in my older Kujira wings, as per Mike Pedigo’s video on this. Worked really well. No I am going to repeat the process with my Cab mast-to-fuse connection. Have to be careful on how much surface area you choose to treat at a time. I will not do the whole “buried” section of mast in one treatment. Especially tricky with that Cabrinha cross-bolt position needing to be pretty accurately located.
I tightened the heads of many masts. The brand I was riding at the time, shipped a few new carbon masts with loose fitting fuselages. When the heads did wear down, it was a super easy fix. Same as tightening a new one with loose fit. I also become suspicious of the aluminum fuselage sockets stretching out with age. The good news, super easy fix. To tighten just a little bit, wipe epoxy on one side of the mast head with your finger. Use a brush to add a little heavier coat. Always sand the shine off the cured epoxy to make it SLIDE on better. Glossy epoxy will prevent it from sliding. For even more tightening, add one layer of fiber glass. The best way is to use masking tape on the head, to make sure you only get epoxy where you want it. If the mast head is loose enough to add one layer of 4 oz glass to one side, that is the best way, and the most durable, long lasting. When applying just epoxy, no glass (because you only need a tiny bit of tightening) the epoxy might chip off over time. A long time, so no worries. You’re now an expert at keeping everything tight for life. This is the beauty of the mast head and socket design. You can retighten with wear. Unlike some socket designs, where they keep adding more screws to hide the poor early design choice. Armstrong, that’s you.
@FSM: if I’m understanding you here, gingerly coat the masthead only and let it cure by itself; NO mold release compound inside aluminum fuselage, NO inserting the epoxy-wetted mast in to the fuselage to later pound off with a rubber mallet?
You guess at how much to add to the mast head. Just barely loose, just paint one side of head with epoxy. Pretty dam loose, add one layer of 4ox glass. After it cures, simply sand face of head to make it fit. It’s very easy to sand with sandpaper on wood block and dial in the tightness you want. No need to fear adding too much to the mast head. It will sand right back down super easy to dial in the prefect tight fit.
Never put the fuselage on until epoxy is hard and lightly sanded.
Honestly, do it once, and you’ll understand any idiot can do it and get a wonderful fit.
Don’t use 5 minute epoxy. It’s garbage and chips off too easy. Only use the 5 minute stuff, if away on vacation, and you need a desperate fix.
Absolutely don’t put any epoxy on the skinny end. Just the big flat side faces. One side is usually enough.
Here is a picture of a worn out GoFoil getting tightened. Same technique. Tape it off, then add epoxy.
Are you sure it’s worn and that’s why it’s wiggling and the fuse isn’t cracked? That has been known to happen.
Also, another easy solution is to remove a fraction of a mm from the very bottom of the mast so it can sit deeper and tighter in the socket.
Different sport, same problem. A windsurf powerbox fin was bit loose so coated side of box with vaseline, painted head of fin with epoxy wrapped with one layer of cling film and screwed lightly into place. After setting was relieved it came apart, sanded smooth and fitted perfect. Had a very loose fin for US box so coated both sides with 4oz fibre glass and sanded with block until it fitted, the blox smooths any high points first.
